The high power efficiency of class D push-pull amplifiers is well known, and it is also known that in order to achieve an ideal 3-state PWM output signal, a low impedance return path must be provided, during periods when neither of the push-pull amplifiers is conductive, for energy stored in magnetic and capacitive components of the load on the equipment.
This has been done to some degree by use of snubbing networks, which dissipate excessive power, or by use of high voltage transistors selectively activated and configured in a conventional amplifier bridge circuit, but additionally having somewhat involved drive requirements due to ground reference conditions.